<template>
  <div class="slider" ref="slider">
    <div class="slider-group" ref="sliderGroup">
      <slot></slot>
    </div>
    <div class="dots">
      <span class="dot" v-for="(item, index) in dots" :key="index" :class="{active : currentPageIndex === index}"></span>
    </div>
  </div>
</template>

<script type="text/ecmascript-6">
import { addClass } from 'common/js/dom'
import BScroll from 'better-scroll'
export default {
  data () {
    return {
      dots: [],
      currentPageIndex: 0
    }
  },
  props: {
    // 是否循环轮播
    loop: {
      type: Boolean,
      default: true
    },
    // 自动轮播
    autoPlay: {
      type: Boolean,
      default: true
    },
    // 间隔
    interval: {
      type: Number,
      default: 4000
    }
  },
  mounted () {
    setTimeout(() => {
      this._setSliderWidth()
      this._initDots()
      this._initSlider()
      this._onScrollEnd()
    }, 20)
    // 监听窗口大小改变时间
    window.addEventListener('resize', () => {
      if (!this.slider) {
        return
      }
      this._setSliderWidth(true)
      this.slider.refresh()
    })
  },
  destroyed () {
    clearTimeout(this.timer)
  },
  methods: {
    _setSliderWidth (isResize) {
      // 获取整个列表的的子元素
      this.children = this.$refs.sliderGroup.children
      let width = 0
      // slider 可见宽度
      let sliderWidth = this.$refs.slider.clientWidth
      for (let i = 0; i < this.children.length; i++) {
        let child = this.children[i]
        // 设置每个子元素的样式及高度 每一个都添加一个slider-item
        addClass(child, 'slider-item')
        child.style.width = sliderWidth + 'px'
        // 计算总宽度
        width += sliderWidth
      }
      // 循环播放首尾各加一个,因此总宽度还要加两倍的宽度
      if (this.loop && !isResize) {
        width += 2 * sliderWidth
      }
      this.$refs.sliderGroup.style.width = width + 'px'
    },
    _initSlider () {
      // 定义slider
      this.slider = new BScroll(this.$refs.slider, {
        scrollX: true,
        scrollY: false,
        momentum: false,
        snap: {
          loop: this.loop,
          threshold: 0.3,
          speed: 400
        },
        snapSpeed: 400,
        bounce: false,
        stopPropagation: true,
        click: true
      })
      this.slider.on('scrollEnd', this._onScrollEnd)
    },
    _onScrollEnd () {
      let pageIndex = this.slider.getCurrentPage().pageX
      this.currentPageIndex = pageIndex
      if (this.autoPlay) {
        this._play()
      }
    },
    _play () {
      clearTimeout(this.timer)
      this.timer = setTimeout(() => {
        this.slider.next()
      }, this.interval)
    },
    _initDots () {
      // 长度为n的空数组
      this.dots = new Array(this.children.length)
    }
  }
}
</script>

<style lang="stylus" scoped rel="stylesheet/stylus">
  @import '~common/stylus/variable';

  .slider {
    min-height: 1px;
    position: relative;

    .slider-group {
      position: relative;
      overflow: hidden;
      white-space: nowrap;

      .slider-item {
        float: left;
        box-sizing: border-box;
        overflow: hidden;
        text-align: center;

        a {
          display: block;
          width: 100%;
          overflow: hidden;
          text-decoration: none;
        }

        img {
          display: block;
          width: 100%;
        }
      }
    }

    .dots {
      position: absolute;
      right: 0;
      left: 0;
      bottom: 12px;
      text-align: center;
      font-size: 0;

      .dot {
        display: inline-block;
        margin: 0 4px;
        width: 8px;
        height: 8px;
        border-radius: 50%;
        background: $color-text-l;

        &.active {
          width: 20px;
          border-radius: 5px;
          background: $color-text-ll;
        }
      }
    }
  }
</style>
